1. Field of the Invention
The present invention relates to seek pattern formation circuits, and more particularly relates to a seek pattern formation circuit which includes a seek pattern shaping circuit for selectively eliminating narrow pulses when a step pulse period is shortened and some pulses included in a predetermined pulse train forming a seek pattern become very narrow.
2. Description of the Related Art
In general, in floppy disk drives (FDDs) and the like, a stepping motor, which is driven by a stepping motor driver, is used to move a head to a predetermined writing or reading position on a floppy disk. A seek pattern formation circuit is used to energize the stepping motor driver.
FIG. 7 shows an example of the structure of a conventional seek pattern formation circuit.
As shown in FIG. 7, a seek pattern formation circuit 70 includes a step pulse detection circuit 71 for detecting a step pulse supplied from a host computer (not shown) and outputting the step pulse; a seek pattern generation circuit 72 for generating a seek pattern formed of a plurality of predetermined pulses, that is, a pulse train, every time the step pulse is applied; and a distributing circuit 73 for distributing and supplying the seek pattern to a stepping motor driver 74. The stepping motor driver 74 rotates and drives a stepping motor (STM) 75 in response to the supplied seek pattern.
FIG. 8 includes waveform diagrams showing examples of seek patterns output from the seek pattern formation circuit 70.
Referring to FIG. 8, a first waveform and a third waveform from the top show waveforms of step pulses (STEPs) which are supplied to the seek pattern generation circuit 72. A second waveform and a fourth waveform from the top show waveforms of seek patterns (A) which are output from the seek pattern generation circuit 72. Concerning the first and second waveforms from the top, the period for which the step pulse is applied is longer than the period for which the seek pattern is generated. Concerning the third and fourth waveforms from the top, the period for which the step pulse is applied is shorter than the period for which the seek pattern is generated.
As shown in FIG. 8, the seek pattern generation circuit 72 generates and outputs a new seek pattern every time a step pulse is applied. Every time the step pulse is applied, the polarities of pulses in the seek pattern are inverted.
In the conventional seek pattern formation circuit 70, a step pulse supplied from the step pulse detection circuit 71 to the seek pattern generation circuit 72 is obtained in response to the step pulse detection circuit 71 detecting the step pulse supplied thereto from the host computer (not shown). The step pulse period does not correspond to the operating period of the FDD. As a result, the period for which the step pulse is applied to the seek pattern generation circuit 72 may be less than the period for which the seek pattern is generated.
For example, as indicated by the first and second waveforms from the top in FIG. 8, when the period for which the step pulse is applied is longer than the period for which the seek pattern is generated, the seek pattern generation circuit 72 generates all of the pulses forming the seek pattern every time the step pulse is supplied and supplies the normal seek pattern to the stepping motor driver 74 through the distributing circuit 73. In contrast, as indicated by the third and fourth waveforms from the top in FIG. 8, the period for which the step pulse is applied is shortened. Thus, the period for which the step pulse is applied is shorter than the period for which the seek pattern is generated. In this case, the seek pattern generation circuit 72 sequentially generates pulses forming the seek pattern every time the step pulse is supplied. Since the next step pulse is supplied before all the pulses forming the seek pattern are generated, the seek pattern output from the seek pattern generation circuit 72 may have less pulses than the normal pattern. Not only is the number of pulses smaller, but also the last pulse width may be narrower than the normal pulse width.
In the conventional seek pattern formation circuit 70, when the output seek pattern is supplied to the stepping motor driver 74, and when pulses having a width which is much narrower than the normal pulse width are included in the seek pattern, the narrow pulses may induce noise, and this in turn may cause a malfunction in the stepping motor driver 74.
Accordingly, it is an object of the present invention to provide a seek pattern formation circuit capable of eliminating, from an output seek pattern, pulses having a width which is much narrower than the normal pulse width when the period for which the seek pattern is generated becomes shorter than the period for which the step pulse is applied.
In order to achieve the foregoing objects, a seek pattern formation circuit according to the present invention includes a seek pattern generation circuit that generates a seek pattern having a predetermined pulse train every time a step pulse is applied. The pulse train includes pulses having normal pulse widths. A seek pattern shaping circuit shapes the seek pattern output from the seek pattern generation circuit and supplies the seek pattern to a stepping motor driver. When the period for which the step pulse is supplied becomes shorter than the period for which the seek pattern is generated, and when at least one of the pulses included in the pulse train of the seek pattern becomes narrower than the normal width of that pulse, the seek pattern shaping circuit selectively eliminates the at least one narrow pulse.
Accordingly, when the period for which the step pulse is applied becomes shorter than the period for which the seek pattern is generated, and when a pulse having a width which is much narrower than a predetermined pulse width is included in the seek pattern output from the seek pattern generation circuit, the seek pattern shaping circuit is connected to the output side of the seek pattern generation circuit, and hence the seek pattern shaping circuit eliminates only a narrow pulse. Accordingly, a narrow pulse, which may induce noise, is prevented from being supplied to the stepping motor driver, and hence a malfunction in the stepping motor driver is prevented.
The narrow pulse may have a width narrower than the width of two clock pulses or may have may a width narrower than one clock pulse.
The seek pattern shaping circuit may also comprise feedback between an output of the seek pattern shaping circuit and the seek pattern shaping circuit. The seek pattern may be shaped only when the predetermined frequency of the applied step pulses is higher than the frequency at which the seek pattern is generated.
Accordingly, it is possible to eliminate only a very narrow pulse, from among narrow pulses, which may cause induced noise.